1. Technical Field
The present disclosure relates to a nonaqueous electrolytic solution, and a lithium ion secondary battery including the same.
2. Related Art
Lithium ion secondary batteries are lighter in weight and higher in capacity than nickel-cadmium batteries, nickel-metal hydride batteries, and the like. The lithium ion secondary battery has been therefore widely used as a power source for a mobile electronic appliance. Further, as the mobile electronic appliances decrease in size and increase in functionality in recent years, the lithium ion secondary battery has been expected to have further higher capacity. Not just for the mobile electronic appliances, furthermore, the high-capacity lithium ion secondary battery has been a strong candidate as a power source to be mounted on a hybrid vehicle, an electric vehicle, or the like. In addition, along with the recent size reduction and sophistication in functionality of mobile electronic appliances, the lithium ion secondary battery serving as a power source for these appliances has been expected to have further higher capacity. A lithium ion secondary battery mainly includes, for example, a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution. Various studies have been conducted for further improving the battery characteristics of the lithium ion secondary battery.
For example, the nonaqueous solvent in the nonaqueous electrolytic solution preferably has a relatively low melting point, a relatively high conductivity, and a relatively wide potential window (electrochemical window). It is also preferred that the nonaqueous solvent can be provided with high ion conductivity even at low temperature when an electrolyte is dissolved therein. From this viewpoint, therefore, propylene carbonate is preferably used as the nonaqueous solvent. However, when the negative electrode contains a carbon material such as highly crystallized graphite, there is a problem that the decomposition of propylene carbonate progresses at a cathode (electrode that serves as a negative electrode during discharging) especially during charging.
The progress in decomposition of propylene carbonate causes gas emission, and, with the gas emission, separation and/or decomposition of the carbon material of the negative electrode or the like occurs. This results in a problem that, during the usage, the battery characteristics such as capacity and charging/discharging cycle characteristics gradually deteriorate. Moreover, the progress in decomposition of propylene carbonate causes a decomposition product to be deposited on the negative electrode. This deposited material may further deteriorate the above battery characteristics.
It has therefore been proposed that 1,3-propane sultone or 1,4-butane sultone be added as a nonaqueous solvent to a nonaqueous electrolytic solution containing propylene carbonate (see, for example JP-A-2000-3724 and JP-A-2000-3725). The addition of such a nonaqueous electrolytic solution intends to suppress the progress of decomposition reaction of propylene carbonate as mentioned above.